The invention relates to an injection molding nozzle for hot channel injection molds, comprising a nozzle body which has a mass flow channel for a melt provided at one end with a nozzle discharge opening and, at its other end, with a supply opening arranged at the side of the nozzle body through which a valve needle extends for controlling the discharge of the melt from the nozzle opening.
Such a hot channel nozzle is known, for example, from DE 199 50 273 C1. In the known hot channel nozzle, which is generally installed in an injection molding tool, molten plastic is conducted via channels arranged in the injection molding tool by way of the side supply openings to the mass flow channel. By way of the mass flow channel, which is generally filled with melt, the melt reaches the nozzle discharge opening. When the valve needle opens the nozzle discharge opening, melt can flow into the mold disposed adjacent the nozzle discharge opening. When the valve needle closes, the discharge opening the melt is retained in the mass flow channel. Instead of closing the nozzle discharge opening by the valve needle, also a connecting passage in the injection molding may be closed. In that case, the nozzle discharge opening serves as guide structure for the valve needle.
In order to achieve a high quality for the injection molded parts, it is very important that the melt has a homogeneous consistency. However, the homogeneous consistency which may still be present at the supply opening may be disturbed by the valve needle disposed in the mass flow channel. Since the melt enters the mass flow channel through side openings, it impinges onto the valve needle whereby the melt flow is divided into two parts. Although the two partial flows meet again behind the valve needle, flow lines can be formed. Such flow lines are very objectionable since the flow lines are optically apparent in the injection-molded component and may result in discarding the product. Furthermore, in remote areas of the mass flow channel, melt material may be retained in the known hot channel nozzles and re-entrained into the melt flow at a later time, whereby the homogeneous consistency is also much disturbed.
WO 01/34365 A1 discloses a mixing device for injection molding machines which includes a mass flow channel for plastic material melts with a supply opening arranged at a front end and an outlet opening at the opposite end. In the mass flow channel a cylindrical closure element is disposed by which the outlet opening can be closed.
The closure element or valve needle extends through a bushing whose outer wall is disposed closely adjacent the mass flow channel. At the inner wall, the sleeve is provided with a groove which extends spirally over the full length of the sleeve and which forms a channel with the wall of the mass flow channel. The web formed between two adjacent grooves of the spiral groove structure is disposed at the end of the sleeve remote from the outlet opening of the sleeve tightly on the closure element at least over a full turn. In this way, the melt can reach the outlet opening only through the groove or, respectively, the closed channel formed by means of the closure element.
However, in the direction toward the outlet opening a continuously increasing gap is formed between the web and the closure element so that the melt can flow through that gap also in axial direction to the outlet opening. In this way, a good mixture of the melt is to be obtained. The problem encountered with a side admission opening for the melt however cannot be eliminated by the known mixing element.
It is the object of the invention to provide a hot channel nozzle of the type referred to above in such a way that the melt is delivered with a very high homogeneous consistency.